Chemistry Unit 2 Chemical Bonds

For this exam you need to know about the three types of bonds, covalent, ionic and metallic.

Q) What is the reason why chemical bonding occurs?

• Chemical bonding takes place to increase the number of protons in the nucleus.

• Chemical bonding takes place to increase the number of neutrons in the atoms nucleus

• Chemical bonding occurs because atoms need a full outer shell of electrons to become stable.

The ionic bond is the electrostatic force of attraction between a positively charged metal ion and a negatively charged non-metal ion.

Metals form positive ions because they lose electrons to become stable. While non-metal forms a negative charge as they gain electrons.

What type of elements will you find ionic bonding taking place between?

• Metal and metal

• non-metal and non-metal

• metal and non-metal?

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A covalent bond is formed when two atoms share a pair of electrons. Covalent bonding occurs in most non-metal elements, and in compounds formed between non-metals.

These shared electrons are found in the outer shells of the atoms. Usually each atom contributes one electron to the shared pair of electrons.

Q) Which group is oxygen in and how many more electrons does it need to gain to have a full outer shell?

• 1

• 2

• 3

• 4

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Metallic bonding occurs between the atoms of metal elements - Lithium, Berrylium, Sodium, Magnesium, Aluminium and Calcium. The outer electrons are delocalised (free to move).

This produces an electrostatic force of attraction between the positive metal ions and the negative delocalised electrons.

This delocalised 'sea of electrons' is responsible for metal elements being able to conduct electricity.

Q) What do metal atoms share?

• Metal atoms share delocalised electrons.

• Metal atoms share protons

• Metal atoms share neutrons

Explain the term "delocalised electrons"

• The delocalised electrons take part in ionic bonding

• The delocalised electrons are free to move

• The delocalised electrons can only vibrate in one position.

• The delocalised electron take part in covalent bonding

Ionic bonding forms between positive and negative ions.

What can you tell about the ionic bonding by looking at image of sodium chloride?

• Sodium being in group 1 has lost an electron to form a positive ion while chlorine being in group 7 has gained an electron to form a negative ion. They are held together by a strong electrostatic force.

• Sodium has gained an electron to form a negative ion

• Chlorine has lost an electron to form a positive ion.

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Ionic bonding is the transfer of electron from the metal to a non metal as shown on the diagram.

When do non metal form a negative ion?

• Negative ions are formed when it gains electrons.

• Negative ions are formed when an atom loses an electron.

• Negative ions are formed when a neutron becomes an eletron

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Covalent bonding is a shared pair of electrons. These electrons are shared between two atoms to form a strong bond.

Covalent bond forms between non metal atoms.

Only the electrons in the outermost electron can be shared.

Look at the image of carbon dioxide (CO₂). How many electrons are each oxygen sharing with carbon?

The share electrons so both carbon and oxygen get full outershell, which is to have 8 electrons.

Oxygen needs to more and carbon requires 4 more.

• 3

• 2

• 1

• 4

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Nitrogen is in group 5 so has 5 electrons in the outer shell.

Nitrogen needs 3 more electron to get full outershell. Full outershell is when the atom gets 8.

Hydrogen has an atomic number of 1 so has one electron. For hydrogen to get full outershell it requires 1 more electron. Hydrogen needs one more electron as its outer electron is in the first shell. The first shell gets filled up by 2 electron.

Q) How many shared electron does the nitrogen get when it forms the ammonia molecule. (NH₃)

• 3

• 1

• 2

• 7

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Most metals have between one and three electrons in their outershell, (except transition metals). These electrons are delocalosed which means they are not in a fixed position and move around the structure of the metal.

As the electrons move they are shared within the structure. The metallic bond formed are from the attraction between positively charged nuclei and the negatively charged electrons.

Q) Look at the image of the metallic bonding, describe what the large circle represents and what the small circle represents.

• Positive atomic nuclei (orange circles) surrounded by a sea of delocalised electrons (yellow circles).

• The large circle is the neutrons

• The large circles are the protons

• The small circle represents the nucleus.

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